Table saws are used in the construction and wood working industries. When a saw blade of a table saw comes in contact with a workpiece, e.g., a piece of lumber, to cut the workpiece, the height and angle of the blade relative to the workpiece determines the depth and angle of cut into the workpiece. Because workpieces vary significantly in size and desired cut types, it is advantageous to make saw blades adjustable relative to the work surface of the table saw, and thus adjustable relative to the workpiece supported by the work surface. An example of a prior art table saw with a height adjustment mechanism is depicted in FIG. 1.
The table saw 10 depicted in FIG. 1 includes a housing 11 supporting a table top work surface T with a saw blade S projecting through an opening O defined in the surface. The saw blade S is supported for rotation by a carriage 12 adjustably supported within the housing 11, with the carriage configured to carry a drive motor (not shown) for rotating the saw blade. The table saw 10 may further include a table extension and a rip fence as depicted in FIG. 1. The table saw 10 further includes an on/off or power switch P for energizing the drive motor to operate the saw blade. The particular position of the saw blade S relative to the table top T may be adjusted by rotating a crank wheel 14 of a height adjustment mechanism that interacts with the carriage 12 through worm gears, bevel gears, or other kinematic sliding mechanisms of the table saw 10 to adjust the vertical position V of the saw blade S. The power tool 10 further includes a bevel adjustment mechanism 15 that can be manually actuated to slide the height adjustment mechanism 14 along a curved slot 16 formed in the housing 11 to pivot the saw blade S in the direction of the arrows B. In some power tools the table top T is adjusted while the position of the blade remains vertical. In those types of power tools, the adjustment mechanisms 14, 15 may be configured to raise/lower or tilt the table top relative to the saw blade. The end result of either approach (i.e., moving the blade or moving the table top) is that the saw blade contacts the workpiece at a different height or angle.
Both adjustments of the saw blade S, vertical and bevel angle, are typically tedious and time consuming, and both mechanisms 14, 15 are difficult use to provide fine adjustments. For instance, fine vertical adjustments V require repetitive manual turning of the crank. Further, the process is imprecise and can require substantial effort to achieve the precise saw blade configuration that is desired. Finer adjustments can be accomplished by using finer toothed gearing, but at the cost of even more turning of the crank. Additionally, in some circumstances, the workpiece may not have a uniform thickness, creating difficulty to the user in manually adjusting the height or bevel angle during operation of the table saw.
Consequently, there is a need for adjustment mechanisms for the saw blade of a power tool that is easier and less time consuming to operate and that can accomplish fine adjustments. Power tools, such as power table saws, planers, miter saws, vertical saws, bevel saws, circular saws, or the like have evolved through the years to incorporate various safety mechanisms, such as blade guards, that try to prevent the operator from contacting the moving tool during an operation.
Most power tools include an on/off switch that is used by the operator to turn the power tool on and to shut the tool off after an operation is completed. The problem with the power switch is that it requires the operator to manually de-activate the switch after the cutting operation is complete, but while the tool is still operating or the saw blade is still spinning During the cut the operator's attention is fixed on the task at hand, namely to guide the workpiece through the working saw blade at a consistent horizontal speed to produce a clean cut. Once the cut is complete the operator's attention is naturally on the finished product, at a minimum to move the separated pieces of the workpiece from the working space around the cutting blade. The operator's attention is then diverted to finding the power switch to deactivate the power tool, all while the saw blade is continue to run.
Even the most attentive craftsman is prone to lapses in attention once the cut has been finished. Consequently there is a need for a need for a power tool that incorporates a feature that automatically shuts off the drive motor to the tool after a cutting operation has been completed or under other conditions indicating that the cutting tool should be de-activated.